A description will be given of the immunochromatographic assay. An immunochromatographic test strip is a test strip preliminarily coated with a bandlike coating of an antibody (or antigen) which brings about an antigen-antibody reaction with an antigen (or antibody) in analyte (sample), at a specific location on the test strip. After the analyte is applied to the immunochromatographic test strip, the antigen (or antibody) in the analyte is dissolved into a developing solution and migrates on the test strip, and the antigen (or antibody) in the analyte comes to bring about the antigen-antibody reaction at the location of the antibody (or antigen) coating on the immunochromatographic test strip, to be trapped. Since an amount of the antigen (or antibody) thus trapped is the total amount of the antigen (or antibody) in the analyte, the total amount of the antigen (or antibody can be measured by optical measurement in a way of labeling the antigen (or antibody) in the analyte with a dye and measuring the absorbance or the like thereof. The immunochromatographic assay is a method enabling quantitative determination of even an extremely fine amount when compared with the ordinary color test methods.
One of known devices for measuring a concentration of a specific substance in analyte from an immunochromatographic test strip after development and coloring of the analyte is a device configured to reflect measurement light emitted from an LED, on the immunochromatographic test strip and to measure the reflected light with a photodiode through one hole for guiding the reflected light (e.g., reference is made to Patent Document 1).
[Patent Document 1] Japanese Patent Application Laid-Open No. 11-83745 (p4)